A member of the North Korean leader's security team was seen wearing white gloves and wiping down the Trump-branded pen provided for him moments before the two leaders sat down to put their names to the agreement.

Then at the last moment Mr Kim’s sister, Kim Yo-jong, pulled a pen from her pocket which she gave to her brother.

The moment came as Mr Kim and Mr Trump signed an agreement at the The Capella Resort on the Singapore island of Sentosa , which committed to "leave the past behind" with North Korea pledging to start decommissioning parts of its nuclear arsenal.

Despite the unprecedented rapprochement between the two countries, the North Koreans have maintained a tight security presence around their leader.

Mr Kim is notoriously paranoid about leaving behind person and biological information about himself when he travels abroad.

Anyone else spot this? There were two "Donald Trump" signing pens, NK official came in and shined up the one for Kim, then at the last minute Kim Yo Jong pulled out her own per to use instead of the one provided. Kim used that and back it went in her blazer. (Pool video) pic.twitter.com/dZWEK22IdF

He is reported to have brought his own toilet with him to the summit at the island hotel so that he doesn't leave any stool behind that can be analysed for intelligence about his health.

Paranoia about leaving behind DNA evidence is not confined to Mr Kim as his father, Kim Jong-il, also brought a private toilet with him when he travelled.

Lee Yun-keol, a North Korean defector who worked in the regime’s Guard Command unit before escaping to South Korea in 2005, told the Washington Post: “Rather than using a public restroom, the leader of North Korea has a personal toilet that follows him around when he travels.

Trump-Kim summit in pictures: Best photos from Donald Trump and Kim Jong-un's meeting in Singapore

“The leader’s excretions contain information about his health status so they can’t be left behind”.

He is also known to be a heavy smoker and is frequently seen holding a lit cigarette in official photographs.

Information about the Kim family is so tightly controlled by North Korea that basic facts about Mr Kim such as his age, he is thought to be 34, and the number of children he has are not known for certain.

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North Korea has deployed other tight security measures to protect the leader while at the summit such as using decoy planes, bringing their own food and transporting him in a bullet-proof limousine.

Although yesterday Mr Kim did break with his closely-guarded regime when he went for a night-time stroll on the Singapore waterfront, even posing for selfies with the city-state's foreign minister.